Composition for improving the property of a golf ball cover

ABSTRACT

Disclosed is a golf ball cover property improving composition to be added to a thermoplastic polymer material such as a thermoplastic polyurethane material when a golf ball cover is formed from the thermoplastic polymer material, to thereby impart high restitution and excellent scuff resistance to the golf ball cover. The golf ball cover property improving composition contains an isocyanate mixture in which an isocyanate compound (X) having at least two isocyanate groups serving as functional groups in the molecule is dispersed in a thermoplastic resin (Y) which is substantially non-reactive with the isocyanate groups and which has a restitution elastic modulus of at least 45%.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a composition for improving the property of a golf ball cover (hereinafter the composition will be referred to as a “golf ball cover property improving composition”), which is employed when a golf ball cover is formed from a thermoplastic polymer material; and more particularly to a golf ball cover property improving composition for being added to a thermoplastic polymer material when a golf ball cover is formed predominantly from the polymer material, the polymer material being virtually reactive with an isocyanate group contained in the composition. The golf ball cover property improving composition serves as a cross-linking agent for the polymer material.

[0003] 2. Description of the Related Art

[0004] In recent years, polyurethane materials have become of interest as materials for forming a golf ball cover. Polyurethane materials are classified into thermosetting polyurethane materials and thermoplastic polyurethane materials, and a process for forming a thermosetting polyurethane material into a product differs from a process for forming a thermoplastic polyurethane material into a product. A thermosetting polyurethane material can be formed into a product through the following procedure: a urethane prepolymer having an isocyanate end group and a curing agent such as polyol or polyamine, which serve as liquid raw materials, are mixed under heating; and the resultant mixture is fed directly to a mold and then heated, to thereby allow urethane curing reaction to proceed.

[0005] Many studies have heretofore focused on golf balls formed from thermosetting polyurethane materials. For example, U.S. Pat. Nos. 5,334,673, 6,117,024, and U.S. Pat. No. 6,190,268 disclose such golf balls. Meanwhile, U.S. Pat. Nos. 5,006,297, 5,733,428, 5,888,437, 5,897,884, and U.S. Pat. No. 5,947,843 disclose forming methods of thermosetting polyurethane materials.

[0006] Since a thermosetting polyurethane material exhibits no thermoplasticity, the material and a product formed from the material cannot be recycled. In addition, when a thermosetting polyurethane material is employed for forming a specific product such as a golf ball cover (i.e., a product which covers a core), efficient production of the product is not attained, since the heating-curing step and the cooling step of the material requires long time, and high reactivity and instability of the material make control of the molding time very difficult.

[0007] In the case where a thermoplastic polyurethane material is formed into a molded product, the product is not directly obtained through reaction of raw materials, but is formed from a linear polyurethane material—an intermediate—which has been synthesized by employment of raw materials and a synthesis method, the raw materials and the method differing from those employed in the case of the aforementioned thermosetting polyurethane material. Such a linear polyurethane material exhibits thermoplasticity, and is cured through cooling. Therefore, such a polyurethane material can be molded by use of an injection molding machine. Injection molding of a thermoplastic polyurethane material is a technique suitable for forming a golf ball cover, since the molding time of a thermoplastic polyurethane material is much shorter than that of a thermosetting polyurethane material, and a thermoplastic polyurethane material is suitable for precise molding. Meanwhile, a thermoplastic polyurethane material can be recycled, and is thus environmentally friendly. U.S. Pat. Nos. 3,395,109, 4,248,432, and U.S. Pat. No. 4,442,282 disclose golf balls formed from thermoplastic polyurethane materials.

[0008] However, when a golf ball cover is formed from a conventional thermoplastic polyurethane material, the resultant golf ball is not satisfactory in terms of feeling on impact, controllability, restitution, and scuff resistance upon being hit with an iron.

[0009] In order to solve such a problem, Japanese Patent Application Laid-Open (kokai) No. 9-271538 discloses a golf ball cover formed from a thermoplastic polyurethane material exhibiting high restitution. However, the disclosed golf ball cover is not satisfactory in terms of scuff resistance upon being hit with an iron.

[0010] Japanese Patent Application Laid-Open (kokai) No. 11-178949 discloses a golf ball cover exhibiting relatively excellent scuff resistance upon being hit with an iron, which predominantly contains a reaction product formed from a thermoplastic polyurethane material and an isocyanate compound. When the cover is formed, an isocyanate compound such as a diisocyanate or a block isocyanate dimer, serving as an additive, is added to a thermoplastic polyurethane material in the course of heating, melting, and mixing by use of an extruder, or in the course of injection molding, to thereby allow reaction to proceed.

[0011] However, in the case of molding of the cover disclosed in Japanese Patent Application Laid-Open (kokai) No. 11-178949, since an isocyanate compound must be handled with great care due to its inactivation by moisture, obtaining a stable reaction product is difficult. Meanwhile, a block isocyanate exhibiting moisture resistance is not suitable for forming the cover, since a blocking agent issues a strong odor when the isocyanate is thermally dissociated. When an isocyanate compound assumes the form of powder or solution, control of the amount of the compound which is added to a thermoplastic polyurethane material is difficult, and therefore cover properties cannot be controlled adequately. In addition, since the thermoplastic polyurethane material differs in melting point and melt viscosity from the isocyanate compound, thorough and satisfactory kneading thereof may fail to be attained in a molding apparatus. Therefore, in the technique disclosed in the above publication, the effect of moisture on a cover material and the amount of an additive is not satisfactorily controlled, resulting in failure to produce a golf ball cover which is satisfactory in terms of improvement of scuff resistance.

[0012] Japanese Patent Application Laid-Open (kokai) No. 11-178949 discloses an aliphatic isocyanate-based thermoplastic polyurethane material to be used as a desirable thermoplastic polyurethane material. However, since the thermoplastic polyurethane material is highly reactive with isocyanate and its reaction is difficult to control, the polyurethane material involves the following problems: gelation easily occurs before injection molding, and sufficient plasticity cannot be maintained; gelation may occur during molding of a cover; and the polyurethane material cannot be recycled, due to gelation. Because of such problems, the thermoplastic polyurethane material is difficult to use in practice.

[0013] Japanese Patent Publication (kokoku) No. 58-2063 (U.S. Pat. No. 4,347,338) discloses a process for producing a thermosetting polyurethane product, in which a compound having two or more isocyanate groups is mixed with a thermoplastic resin which is non-reactive with an isocyanate group, the resultant mixture is incorporated into a thermoplastic polyurethane material, and the resultant material is subjected to molding by use of a molding machine. However, the purpose of the technique disclosed in the above publication is to improve the polyurethane product only in terms of solvent resistance and durability against continuous, repeating friction, and the publication does not disclose use of the aforementioned forming material as a material of a golf ball cover. There still exists demand for golf ball cover materials which can provide a golf ball with various necessary properties, such as restitution, total distance, spin performance, controllability, feeling on impact, scuff resistance, cut resistance, and discoloration resistance. Moreover, there exists demand for appropriate combination of such golf ball cover materials.

SUMMARY OF THE INVENTION

[0014] In view of the foregoing, an object of the present invention is to provide a golf ball cover property improving composition to be added to a thermoplastic polymer material, such as a thermoplastic polyurethane material, when a golf ball cover is formed from the thermoplastic polymer material, the golf ball cover property improving composition serving as a cross-linking agent for the thermoplastic polymer material and realizing production of a golf ball cover exhibiting high restitution and excellent scuff resistance.

[0015] In order to achieve the above object, the present invention provides the following golf ball cover property improving compositions.

[0016] (1) A golf ball cover property improving composition comprising an isocyanate mixture in which an isocyanate compound (X) having at least two isocyanate groups serving as functional groups in the molecule is dispersed in a thermoplastic resin (Y) which is substantially non-reactive with the isocyanate groups and which has a restitution elastic modulus of at least 45%.

[0017] (2) A golf ball cover property improving composition according to (1), wherein the isocyanate compound (X) is 4,4′-diphenylmethane diisocyanate.

[0018] (3) A golf ball cover property improving composition according to (1) or

[0019] (2), wherein the thermoplastic resin (Y) is a polyester elastomer.

[0020] (4) A golf ball cover property improving composition according to any one of (1) through (3), wherein the ratio by weight of the thermoplastic resin (Y) to the isocyanate compound (X) is 100:5 to 100:100.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0021] The present invention will next be described in more detail. In the present invention, the isocyanate compound (X) having at least two isocyanate groups serving as functional groups in the molecule is preferably an isocyanate compound which is conventionally employed in the technical field related to thermoplastic polyurethane materials. Examples of the isocyanate compound include, but are not limited to, aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as hexamethylene diisocyanate. Of these, 4,4′-diphenylmethane diisocyanate is most preferred, in consideration of reactivity and operational safety.

[0022] The thermoplastic resin (Y) which is substantially non-reactive with isocyanate is preferably a resin exhibiting low water-absorbability and excellent compatibility with a thermoplastic polymer material (described below) to be cross-linked. The thermoplastic resin (Y) must exhibit excellent compatibility with a thermoplastic polymer material to be cross-linked, high restitution elasticity, and high strength. The restitution elastic modulus of the thermoplastic resin (Y) is preferably at least 45%, more preferably at least 50%, much more preferably at least 55%, as measured in accordance with JIS-K7311. When the restitution elastic modulus is lower than 45%, the resultant molded product exhibits considerably low restitution. Therefore, the thermoplastic resin (Y) suitable for a thermoplastic polymer material to be cross-linked can be selected in consideration of the aforementioned properties of the resin. For example, when a thermoplastic urethane material is employed as the thermoplastic polymer material, in consideration of the aforementioned properties, the thermoplastic resin (Y) is preferably selected from among polyester elastomers such as ether-ester block copolymers and ester-ester block copolymers.

[0023] In the composition of the present invention, the ratio by weight of the thermoplastic resin (Y) to the isocyanate compound (X) is preferably 100:5 to 100:100, more preferably 100:10 to 100:40. When the ratio of the isocyanate compound (X) to the thermoplastic resin (Y) is excessively low, in the case where a specific amount of the golf ball cover property improving composition of the present invention is added to a thermoplastic polymer material, the effect of the properties of the resin (Y) becomes greater than the effect of the compound (X), resulting in insufficient improvement of scuff resistance and cut resistance of the resultant golf ball cover. In contrast, when the ratio of the isocyanate compound (X) to the thermoplastic resin (Y) is excessively high, in the case where a specific amount of the golf ball cover property improving composition of the present invention is added to a thermoplastic polymer material, the effect of the properties of the resin (Y) becomes low and restitution of the resultant golf ball cover may be improved only insufficiently.

[0024] The composition of the present invention can be obtained through, for example, the following procedure: the isocyanate compound (X) is incorporated into the thermoplastic resin (Y), and the resultant mixture is completely kneaded by use of a mixing roll or a banbury mixer at 130 to 250° C., followed by pelletization or pulverization after cooling. If moisture is present during kneading, most of the isocyanate groups are inactivated through reaction between moisture and isocyanate, and thus the composition no longer functions as a cross-linking agent. Therefore, entering of moisture must be prevented.

[0025] No particular limitation is imposed on the thermoplastic polymer material to which the composition of the present invention is added during molding of a golf ball cover; i.e., the thermoplastic polymer material which is virtually reactive with isocyanate and which may be employed in combination with the composition of the present invention. However, the thermoplastic polymer material preferably has a polar group such as an amino group, a hydroxyl group, a urea group, or a urethane group. Any thermoplastic polymer material may be employed, so long as the polymer material can cross-link with isocyanate and can be used as a golf ball cover material. Examples of such a thermoplastic polymer material include a thermoplastic polyurethane material, a polyamide elastomer, a modified polyester elastomer, and a resin or elastomer having a polar group, such as ionomer resin. Of these, a thermoplastic polyurethane material is particularly preferred, in consideration of restitution, flexibility, and reactivity with isocyanate.

[0026] The thermoplastic polyurethane material includes soft segments formed of a polymeric polyol (polymeric glycol), a chain extender constituting hard segments, and a diisocyanate. No particular limitation is imposed on the polymeric polyol serving as a raw material, and the polymeric polyol may be any one selected from polymeric polyols which are conventionally employed in the technical field related to thermoplastic polyurethane materials. Examples of the polymeric polyol include polyester polyols and polyether polyols. Of these, polyether polyols are more preferred to polyester polyols, since a thermoplastic polyurethane material having high restitution elastic modulus and exhibiting excellent low-temperature properties can be synthesized. Examples of the polyether polyols include polytetramethylene glycol and polypropylene glycol. From the viewpoints of restitution elastic modulus and low-temperature properties, polytetramethylene glycol is particularly preferred. The average molecular weight of the polymeric polyol is preferably 1,000 to 5,000. The average molecular weight is more preferably 2,000 to 4,000, in order to synthesize a thermoplastic polyurethane material having high restitution elastic modulus.

[0027] Any chain extender which is conventionally employed in the technical field related to thermoplastic polyurethane materials is preferably used. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. The average molecular weight of the chain extender is preferably 20 to 15,000.

[0028] Any diisocyanate which is conventionally employed in the technical field related to thermoplastic polyurethane materials is preferably used. Examples of the diisocyanate include, but are not limited to, aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as hexamethylene diisocyanate. Some diisocyanates involve difficulty in controlling cross-linking reaction during injection molding. In the present invention, 4,4′-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred, in consideration of stability in reaction with the aforementioned composition of the present invention.

[0029] Preferred examples of the thermoplastic polyurethane material containing the aforementioned materials include commercially available polyurethane materials, such as Pandex T-8290, T-8295, and T-8260 (products of DIC Bayer Polymer Ltd.), and Resamine 2593 and 2597 (products of Dainichiseika Color & Chemicals Mfg. Co., Ltd.).

[0030] The ratio by weight of the thermoplastic polymer material which is virtually reactive with isocyanate groups of a thermoplastic polyurethane material, etc. to the composition of the present invention is preferably 100:1 to 100:100, more preferably 100:5 to 100:50, much more preferably 100:10 to 100:30. When the ratio of the composition of the present invention to the thermoplastic polymer material is excessively low, the composition exerts insufficient cross-linking effect, whereas when the ratio is excessively high, unreacted isocyanate imparts a color to the resultant cover-forming material. In the present invention, the cover-forming material may contain other thermoplastic polymer components in addition to the aforementioned components. Examples of such “other thermoplastic polymer components” include polyester elastomer, polyamide elastomer, ionomer resin, styrene block elastomer, polyethylene, and nylon resin. In this case, the incorporation amount of thermoplastic polymer materials other than the aforementioned thermoplastic polymer material which is virtually reactive with isocyanate groups of a thermoplastic polyurethane material, etc. is 0 to 100 parts by weight, preferably 10 to 75 parts by weight, more preferably 10 to 50 parts by weight, on the basis of 100 parts by weight of the thermoplastic polymer material which is virtually reactive with isocyanate groups of a thermoplastic polyurethane material, etc. and which serves as an essential component. The incorporation amount is appropriately determined in accordance with various purposes, including regulation of the hardness of the cover-forming material and improvement of the restitution, fluidity, and adhesion of the cover-forming material. If desired, the cover-forming material may further contain various additives, such as pigments, dispersants, antioxidants, light-resistant stabilizers, UV absorbers, and release agents.

[0031] In use of the composition of the present invention, for example, the composition is added to a thermoplastic polymer material which is virtually reactive with isocyanate groups of a thermoplastic polyurethane material, etc. and then dry-mixed, and the resultant mixture is subjected to injection molding, to thereby form a cover around a core. The molding temperature varies with the type of the thermoplastic polymer material to be employed, but is typically 120 to 300° C.

[0032] When the thermoplastic polymer material is a thermoplastic polyurethane material, in the resultant golf ball cover, reaction or cross-linking is thought to proceed as follows: an isocyanate group is reacted with a residual OH group of the thermoplastic polyurethane material, to thereby form a urethane bond; or an isocyanate group is added to a urethane group of the thermoplastic polyurethane material, to thereby form an allophanate or biuret cross-linking structure. In this case, although cross-linking proceeds insufficiently immediately after injection molding of the cover-forming material, cross-linking proceeds through annealing after injection molding, and the resultant golf ball cover is endowed with useful properties. As used herein, the term “annealing” refers to aging through heating at a certain temperature for a predetermined period of time, or aging at room temperature for a predetermined period of time.

[0033] In the golf ball containing the composition of the present invention, the surface hardness of the cover-forming material is preferably 40 to 80, more preferably 43 to 60, much more preferably 45 to 55, as measured by use of a D-type durometer in accordance with JIS-K6253. When the surface hardness of the cover-forming material is excessively low, the resultant golf ball tends to produce excessive back-spin upon being hit with an iron; i.e., controllability of the golf ball is impaired. In contrast, when the surface hardness of the cover-forming material is excessively high, the resultant golf ball tends to produce insufficient back-spin upon being hit with an iron; i.e., controllability of the golf ball is lowered, and feeling on impact is impaired.

[0034] In the golf ball containing the composition of the present invention, the restitution elastic modulus of the cover-forming material is preferably at least 45%, more preferably 45 to 85%, further preferably 50 to 80%, much more preferably 50 to 60%, as specified by JIS-K7311. Since the thermoplastic polymer material which is virtually reactive with isocyanate, such as a thermoplastic polyurethane material, does not exhibit high restitution, preferably, the restitution elastic modulus is strictly selected. When the restitution elastic modulus of the cover-forming material is excessively low, the total distance of the golf ball is considerably lowered. In contrast, when the restitution elastic modulus of the cover-forming material is excessively high, the initial velocity of the golf ball becomes excessively high when being shot or putted (i.e., when controllability of the golf is required within the range of a total distance of 100 yards or less), and the golf ball may fail to meet a golfer's demand.

[0035] No particular limitation is imposed on the core employed in the golf ball containing the composition of the present invention, and any type of cores that are usually employed can be employed. Examples of the core which may be employed include a solid core for a two-piece ball, a solid core having a plurality of vulcanized rubber layers, a solid core having a plurality of resin layers, and a thread-wound core having a thread rubber layer. No particular limitation is imposed on the outer diameter, weight, hardness, and material of the core. The thickness of the golf ball cover of the present invention preferably falls within a range of 0.1 to 5.0 mm. The cover may have a multi-layer structure, so long as the overall thickness of the cover falls within the above range.

[0036] The golf ball containing the composition of the present invention is formed so as to have a diameter and a weight as specified under the Rules of Golf approved by R&A. Typically, the diameter is at least 42.67 mm, and the weight is 45.93 g or less. The diameter is preferably 42.67 to 42.9 mm. The deformation amount of the golf ball under application of a load of 980 N (100 kg) is preferably 2.0 to 4.0 mm, more preferably 2.2 to 3.8 mm.

EXAMPLES

[0037] The present invention will next be described in detail by way of Examples, which should not be construed as limiting the invention thereto.

Examples and Comparative Examples

[0038] Golf ball cover property improving compositions of the present invention; i.e., compositions 1 through 3 were prepared from components shown in Table 1 (unit: parts by weight). 4,4′-Diphenylmethane diisocyanate (Millionate MT-F, product of Nippon Polyurethane Industry Co., Ltd.) was employed as isocyanate compound (X). The following material was employed as a base resin: an ether-ester block copolymer which had been dried in advance to thereby remove moisture (thermoplastic resin (Y), restitution elastic modulus: 70%), soft vinyl chloride resin pellets which had been dried in advance to thereby remove moisture (plasticizer DOP50PHR, restitution elastic modulus: 35%), or a polystyrene resin which had been dried in advance to thereby remove moisture (restitution elastic modulus: 35%). The above components were mixed sufficiently by use of a tumbler, and the resultant mixture was subjected to extrusion molding by use of a vent-type extruder at 120 to 200° C., to thereby yield strands. After being cooled, the resultant strands were formed into pellets. TABLE 1 Composition 1 Composition 2 Composition 3 Ether-ester block copolymer 70 Soft polyvinyl chloride resin 70 Polystyrene resin 70 4,4′-diphenylmethane diisocyanate 30 30 30

[0039] Core composition Polybutadiene rubber 100 parts by weight Zinc acrylate 21.5 parts by weight Zinc oxide 12 parts by weight Dicumyl peroxide 1 part by weight

[0040] The components of the aforementioned core composition were kneaded, and then subjected to vulcanization and molding at 155° C. for 20 minutes, to thereby obtain a solid core for a two-piece solid golf ball (diameter: 38.5 mm). BRO1 (product of Japan Synthetic Rubber Co., Ltd.) was employed as the polybutadiene rubber. The specific gravity of the thus-obtained core was 1.07; the deformation amount under application of a load of 980 N (100 kg) was 3.4 mm; and the initial velocity as measured by means of a method specified by USGA (R&A) was 78.1 m/s.

[0041] Cover materials shown in Tables 2 and 3 (unit: part(s) by weight) were kneaded by use of a twin-screw extruder at 190° C., to thereby obtain cover-forming materials. Components shown in Tables 2 and 3 are described below.

[0042] Polyurethane 1 (Thermoplastic Polyurethane Material)

[0043] Pandex T8290: MDI-PTMG-type thermoplastic polyurethane material (product of DIC Bayer Polymer Ltd.) (JIS A surface hardness: 93, restitution elastic modulus: 52%)

[0044] Polyurethane 2 (Thermoplastic Polyurethane Material)

[0045] Pandex T8295: MDI-PTMG-type thermoplastic polyurethane material (product of DIC Bayer Polymer Ltd.) (JIS A surface hardness: 97, restitution elastic modulus: 44%)

[0046] Polyurethane 3 (Thermoplastic Polyurethane Material)

[0047] Pandex T8260: MDI-PTMG-type thermoplastic polyurethane material (product of DIC Bayer Polymer Ltd.) (Surface hardness as measured by use of a D-type durometer: 56, restitution elastic modulus: 45%)

[0048] Subsequently, each of the aforementioned solid cores was placed in a mold for injection molding, and a cover (thickness: 2.1 mm) was formed from each of the cover-forming materials—obtained by dry-mixing the cover materials (1) and (2))—around the core by means of injection molding, to thereby produce a two-piece solid golf ball (Examples and Comparative Examples). The resultant golf ball was allowed to stand at room temperature for one week, and then properties of the golf ball were evaluated. The evaluation methods are described below. A sheet (thickness: 2 mm) formed through injection molding was allowed to stand at room temperature for one week, and then subjected to measurement of cover properties. The results are shown in Tables 2 and 3.

[0049] (Cover Properties)

[0050] Surface Hardness

[0051] The surface hardness of the cover was measured by use of a D-type durometer in accordance with JIS-K6253.

[0052] Restitution Elastic Modulus

[0053] The restitution elastic modulus of the cover was measured in accordance with JIS-K7311.

[0054] (Ball Properties)

[0055] Hardness

[0056] The deformation amount of the golf ball under application of a load of 980 N (100 kg) was measured.

[0057] Initial Velocity

[0058] The initial velocity of the golf ball was measured by means of a method specified by USGA (R&A).

[0059] Total Distance

[0060] The golf ball was hit at a head speed of 45 m/s by use of No. 1 wood (a driver) mounted on a swing robot machine, to thereby measure a total distance.

[0061] Scuff Resistance Upon Being Hit With an Iron

[0062] The golf ball was maintained at 23° C., 13° C., or 0° C., and then hit at a head speed of 33 m/s by use of a pitching wedge mounted on a swing robot machine. Thereafter, the scuff resistance of the resultant golf ball was visually evaluated on the basis of the following criteria.

[0063] 5: No scuffing or substantially no scuffing is observed.

[0064] 4: Scuffing is observed, but is negligible.

[0065] 3: The surface of the ball is slightly scaly.

[0066] 2: The surface of the ball is scaly, and a portion between dimples of the cover is lost to some extent.

[0067] 1: A portion between dimples of the cover is completely exfoliated. TABLE 2 Cover material Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 (1) Polyurethane 1 50 Polyurethane 2 50 100 100 100 Polyurethane 3 100 Titanium oxide 3 3 3 3 3 Polyethylene wax 1 1 1 1 1 (2) Composition 1 20 5 10 20 20 Cover Surface hardness 47 47 49 53 58 properties Restitution elastic modulus (%) 50 45 46 48 48 Ball Outer diameter (mm) 42.7 42.7 42.7 42.7 42.7 properties Weight (g) 45.2 45.1 45.2 45.3 45.3 Hardness (mm) 3.3 3.2 3.1 2.8 2.6 Initial velocity (m/s) 77.1 76.9 77 77.2 77.3 Total distance (m) 226 226 227 227 228 Scuff resistance at 23° C. 5 5 5 5 5 at 13° C. 5 5 5 5 5 at 0° C. 4 3 4 4 4

[0068] TABLE 3 Cover material Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 (1) Polyurethane 2 100 100 100 Titanium oxide 3 3 3 Polyethylene wax 1 1 1 (2) Composition 2 20 Composition 3 20 Cover Surface hardness 47 47 47 properties Restitution elastic modulus (%) 35 38 45 Ball Outer diameter (mm) 42.7 42.7 42.7 properties Weight (g) 45.2 45.3 45.1 Hardness (mm) 3.2 3.2 3.2 Initial velocity (m/s) 76 76.3 76.7 Total distance (m) 216 219 224 Scuff resistance at 23° C. 5 5 3 at 13° C. 5 5 2 at 0° C. 4 3 1

[0069] As is clear from Tables 2 and 3, the golf balls of the Examples exhibit high restitution and excellent flight performance, since they contain the composition of the present invention. The results show that the golf balls of the Examples exhibit excellent scuff resistance upon being hit with an iron. In contrast, the golf balls of the Comparative Examples exhibit poor restitution and are not satisfactory in terms of scuff resistance upon being hit with an iron, since they do not contain the composition of the present invention.

[0070] As described above, when the golf ball cover property improving composition of the present invention is added to a thermoplastic polymer material such as a thermoplastic polyurethane material upon molding of a golf ball cover from the thermoplastic polymer material, the resultant golf ball cover exhibits high restitution and excellent scuff resistance. 

What is claimed is:
 1. A golf ball cover property improving composition comprising an isocyanate mixture in which an isocyanate compound (X) having at least two isocyanate groups serving as functional groups in the molecule is dispersed in a thermoplastic resin (Y) which is substantially non-reactive with the isocyanate groups and which has a restitution elastic modulus of at least 45%.
 2. A golf ball cover property improving composition according to claim 1, wherein the isocyanate compound (X) is 4,4′-diphenylmethane diisocyanate.
 3. A golf ball cover property improving composition according to claim 1, wherein the thermoplastic resin (Y) is a polyester elastomer.
 4. A golf ball cover property improving composition according to claim 1, wherein the ratio by weight of the thermoplastic resin (Y) to the isocyanate compound (X) is 100:5 to 100:100. 